PROJECT SUMMARY The 90+ Study (PIs C. Kawas & M. Corrada) was initiated January 1, 2003 as a population? based cohort study of oldest?old survivors of the Leisure World Cohort Study (LWCS, enrollment 1981?1985). One of the largest (1800+ participants) and longest (15+ years) studies of the fastest growing segment of the population, The 90+ Study has contributed important findings about Alzheimer's disease (AD), dementia, cognitive decline, and other outcomes of aging. Since inception, a vital component of our investigations has been The 90+ Autopsy Study. To date, more than 350 autopsies have been completed in the well?characterized participants, and almost 200 participants in the active cohort are currently enrolled, making it one of the largest autopsy studies of the oldest?old in the world. These studies have provided unique insights into clinical?pathological correlates of dementia and successful cognitive aging. With advances in research, a consensus panel of the National Institute on Aging?Alzheimer's Association (Hyman et al. 2012; Montine et al. 2012) proposed updated neuropathological assessments for AD and dementia?related pathologies which were subsequently adopted by the Alzheimer's Disease Centers (ADCs). Responsibility for neuropathologic evaluation for The 90+ Study was transfered to Dr. Tom Montine at Stanford University who has aplied current guidelines. However, the 290 brains accrued before 2017 require updated neuropathologic evaluations. The aims of this administrative supplement are: 1) apply state?of?the?art neuropathological methods according to current NIA?AA neuropathologic guidelines to all autopsied cases from The 90+ Study before 2017 (N=290 brain autopsies) and 2) enter all neuropathological data generated from this supplement for integration into The 90+ Study database and to digitize stained slides of brain tissue from all 90+ autopsied participants (N=350). This effort is a collaboration between UCI (C. Kawas, M. Corrada) and Stanford University (T. Montine, Stanford ADC Pathology Core leader). With standardized, state?of?the art, high quality neuropathological techniques, as well as highly experienced investigators, and a large cohort of well?characterized 90+ individuals, this modest investment will create a unique, modern, and invaluable resource for clinical? pathological investigations of the oldest?old that will be shared with the greater resarch community.